Data Communication & Computer Networks CS 1652 The slides are adapted from the publisher’s material All material copyright J.F Kurose and K.W. Ross, All Rights Reserved Jack Lange University of Pittsburgh 1-1

Course Objectives  Understand modern data communication systems and computer networks  Understand the key concepts  How they are designed & implemented  How they are operated  How they are likely to evolve in the future  Course Approach  Top-down : from what’s familiar to nuts and bolts  The Internet as the main focus  Hands-on experience on networked systems 1-2

Administrativia  Instructor: Jack Lange   Office: Sennott Square #5407  Office Hours: Weds. 2-4PM Teaching Assistant: TBD 1-3

Communication  Course homepage   Announcements, clarifications, corrections  Additional resources for projects  Google Group    Private discussion group Open venue for class discussions and questions  Based on (Pitt addresses) me if you want to use a different one

TextBooks  Computer Networking: A Top-Down Approach  James Kurose and Keith Ross  Fifth/Sixth Edition, Addison Wesley, 2010  TCP/IP Illustrated, Volume I: The Protocols  Richard Stevens  Addison Wesley, 1994

Class meeting times  Lecture  Tues/Thurs: 4:00-5:15PM  Sennott Square, Rm  Lab Sessions  Sennott Square, Rm  Periodically replace lectures  Hands on exercises  Answer project question  Hopefully guest lectures 1-6

Networking Lab  Sennott Square, Rm  16 Linux machines (Fedore Core 13)  Login: Hopefully will be your Pitt login  Available for projects Can use other machines, but… Must work on lab equipment  Dual NICS  1 internal network interface to be used for projects  1 external network interface for external access 1-11

Homework  Reading assignments  Expected to read before each class  Homework  4 problem sets spaced over semester  Projects  Web server (20%)  TCP (50%)  Routing (30%)  Check Syllabus!

Grading  Grading  Midterm (20%)  Final (20%)  4 Homework (10%)  3 Projects (50%)  Late policy  Submit by midnight of the due date  10% penalty for every day late

Projects  Work in groups of 2  C/C++ is required  Lot of work, but will be worth it  Build a TCP stack and a Web server that runs on it  IP routing  Highly Recommended: OS or having some familiarity with Unix systems programming, preferably in C or C++  Minet is in C++  BUILDING software is 50% of the grade of this class 1-9

Today’s topic  Computer Networks Overview  What’s the Internet? Nuts and bolts vs. service view  What’s a protocol? A set of rules between communicating entities  Network edge/core Hosts, access networks, physical media Packet switching/circuit switching, Internet structure  Goal  Get “feel” and terminology  More depth, detail later in course 1-12

What is the internet?  Flows, packets, and bits  Optical light, electricity, and radio waves  Servers, clients, and peers  Hosts, switches, and routers

What’s the Internet: Hardware view  millions of connected computing devices: hosts = end systems Home network Institutional network Mobile network Global ISP Regional ISP router PC server wireless laptop cellular smartphone wired links access points  communication links  fiber, copper, radio, satellite  transmission rate = bandwidth  routers: forward packets (chunks of data) 1-13

What’s a protocol? human protocols:  “what’s the time?”  “I have a question”  introductions … specific msgs sent … specific actions taken when msgs received, or other events network protocols:  machines rather than humans  all communication activity in Internet governed by protocols protocols define format, order of msgs sent and received among network entities, and actions taken on msg transmission, receipt 1-17

What’s a protocol? a human protocol and a computer network protocol: Hi Got the time? 2:00 TCP connection response Get time 1-18 TCP connection request

Where are we?  What’s the Internet?  Nuts and bolts vs. service view  What’s the protocol?  Network edge/core  Hosts, access networks, physical media  Packet switching/circuit switching, Internet structure 1-19

A closer look at network structure:  network edge: applications and hosts  access networks, physical media: wired, wireless communication links  network core:  interconnected routers  network of networks  Edge routers “uplink” to core routers 1-20

The network edge:  end systems (hosts):  run application programs  e.g. Web,  at “edge of network” client/server peer-peer  client/server model  client host requests, receives service from always-on server  e.g. Web browser/server; client/server  peer-peer model:  minimal (or no) use of dedicated servers  e.g. Skype, BitTorrent 1-21 Traditionally where the action is

Internet structure: network of networks  roughly hierarchical  at center: “tier-1” ISPs (e.g., Verizon, Sprint, AT&T, NTT, Quest, Level3, Global Crossing, Tata, Savvis, TeliaSonera), national/international coverage  treat each other as equals Tier 1 ISP Tier-1 providers interconnect (peer) privately 1-13

Internet structure: network of networks  “Tier-2” ISPs: smaller (often regional) ISPs  Connect to one or more tier-1 ISPs, possibly other tier-2 ISPs Tier 1 ISP Tier-2 ISP Tier-2 ISP pays tier-1 ISP for connectivity to rest of Internet  tier-2 ISP is customer of tier-1 provider Tier-2 ISPs also peer privately with each other. 1-15

Internet structure: network of networks  “Tier-3” ISPs and local ISPs  last hop (“access”) network (closest to end systems) Tier 1 ISP Tier-2 ISP local ISP local ISP local ISP local ISP local ISP Tier 3 ISP local ISP local ISP local ISP Local and tier- 3 ISPs are customers of higher tier ISPs connecting them to rest of Internet 1-16

Internet structure: network of networks  a packet passes through many networks! Tier 1 ISP Tier-2 ISP local ISP local ISP local ISP local ISP local ISP Tier 3 ISP local ISP local ISP local ISP 1-17

Tier-1 ISP: e.g., Sprint … to/from customers peering to/from backbone …. … … … POP: point-of-presence 1-14

What’s the Internet: Software-ish view  protocols control sending, receiving of msgs  e.g., TCP, IP, HTTP, Skype, Ethernet  Provides meaning  Internet standards  RFC: Request for comments  IETF: Internet Engineering Task Force  Internet: “network of networks”  loosely hierarchical  public Internet versus private intranet Home network Institutional network Mobile network Global ISP Regional ISP 1-15

What’s the Internet: Service view  communication infrastructure enables distributed applications:  Web, VoIP, , games, e-commerce, file sharing  communication services provided to apps:  reliable data delivery from source to destination  “best effort” (unreliable) data delivery 1-16

Access networks and physical media Q: How to connect end systems to edge router?  residential access nets  institutional access networks (school, company)  mobile access networks Keep in mind:  bandwidth (bits per second) of access network?  shared or dedicated? 1-22

100 Mbps 1 Gbps server Ethernet switch Institutional router To Institution’s ISP Ethernet Internet access  Typically used in companies, universities, etc  10 Mbps, 100Mbps, 1Gbps, 10Gbps Ethernet  Today, end systems typically connect into Ethernet switch 1-32

Wireless access networks  shared wireless access network connects end system to router  via base station aka “access point”  wireless LANs:  b/g (WiFi): 11 or 54 Mbps  n: ~450Mbps  wider-area wireless access  provided by telco operator  ~1Mbps over cellular system (EVDO, HSDPA, 3G)  next up: WiMAX (10’s Mbps) over wide area base station mobile hosts router 1-33

telephone network DSL modem home PC home phone Internet DSLAM Existing phone line: 0-4KHz phone; 4-50KHz upstream data; 50KHz-1MHz downstream data splitter central office Digital Subscriber Line (DSL)  Also uses existing telephone infrastruture  up to 1 Mbps upstream  up to 8 Mbps downstream  dedicated physical line to telephone central office 1-24

Residential access: cable modems Diagram:

Cable Network Architecture: Overview home cable headend cable distribution network (simplified) Typically 500 to 5,000 homes 1-27

Cable Network Architecture: Overview home cable headend cable distribution network server(s) 1-28

Cable Network Architecture: Overview home cable headend cable distribution network (simplified) 1-29

Cable Network Architecture: Overview home cable headend cable distribution network Channels VIDEOVIDEO VIDEOVIDEO VIDEOVIDEO VIDEOVIDEO VIDEOVIDEO VIDEOVIDEO DATADATA DATADATA CONTROLCONTROL FDM (next class): 1-30

ONT OLT central office optical splitter ONT optical fiber optical fibers Internet Fiber to the Home (FTTH)  Optical links from central office to the home  Two competing optical technologies:  Passive Optical Network (PON) – e.g. Verizon FIOS  Active Optical Network (AON) – Switched Ethernet  Much higher Internet rates; fiber also carries television and phone services 1-31

Home networks Typical home network components:  DSL or cable modem  router/firewall/NAT  Ethernet  wireless access point wireless access point wireless laptops router/ firewall cable modem to/from cable headend Ethernet 1-34

Physical media  Bit: propagates between transmitter/rcvr pairs  physical link: what lies between transmitter & receiver  guided media:  signals propagate in solid media: copper, fiber, coax  unguided media:  signals propagate freely, e.g., radio Twisted Pair (TP)  two insulated copper wires  Category 3: traditional phone wires, 10 Mbps Ethernet  Category 5: 100Mbps Ethernet 1-35

Physical media: coax, fiber Coaxial cable:  two concentric copper conductors  bidirectional  baseband:  single channel on cable Digital signal  legacy Ethernet  broadband:  multiple channels on cable Analog Signal  HFC Fiber optic cable:  glass fiber carrying light pulses, each pulse a bit  high-speed operation:  high-speed point-to-point transmission (e.g., 10’s-100’s Gps)  low error rate: repeaters spaced far apart ; immune to electromagnetic noise 1-36

Physical media: radio  signal carried in electromagnetic spectrum  no physical “wire”  bidirectional  propagation environment effects:  reflection  obstruction by objects  interference Radio link types:  terrestrial microwave  e.g. up to 45 Mbps channels  LAN (e.g., Wifi)  11Mbps, 54 Mbps  wide-area (e.g., cellular)  3G cellular: ~ 1 Mbps  satellite  Kbps to 45Mbps channel (or multiple smaller channels)  270 msec end-end delay  geosynchronous versus low altitude 1-37

Summary 1-38  The Internet can be defined as  A set of hosts running distributed applications communicating via routers  Infrastructure providing popular services  Protocols define the message formats, orders, actions on transmission and reception  Access networks: at the network edge  Residential (dial-up, DSL, Cable, FTTH)  Institutional (Ethernet)  Wireless (Wi-fi, WiMAX)

Cable modems  Does not use telephone infrastructure  Instead uses cable TV infrastructure  HFC: hybrid fiber coax  asymmetric: up to 30Mbps downstream, 2 Mbps upstream  network of cable and fiber attaches homes to ISP router  homes share access to router  unlike DSL, which has dedicated access 1-25